Unsymmetrical short-circuit analysis for distribution system considering loads

Amicrogrid is a combination of clusters of distributed generators connected to fulfill the requirement of dedicated load. A microgrid can be operated with standalone or grid connected mode. A microgrid when operated in standalone mode with a limited voltage and power rating is more likely prone to a serious damage due to its unpredictable faults. Load flow, voltage stability & short circuit analysis of a micro-grid is essential for both design and performance monitoring and to ensure reliable microgrid operations. The faults with a continuously varying in nature affects the normal operation of buses and so to the peripherals associated to the micro-grid. The cause and severity of such faults plays a vital role while designing protection scheme in standalone micro-grid as standalone mode has confined generation. In this paper, electrical model of a 52.3 kW Photo-voltaic based micro-grid is developed on Electrical Transient Analysis Program (ETAP) and various transient conditions such as load flow, loss of DG & short circuit analyses are performed. A detailed short circuit analysis puts light on various short circuit conditions and provides useful analysis. ETAP is the most comprehensive analysis platform for the design, simulation, operation, and automation of generation, distribution, and industrial power systems. ETAP also provides the industry leading transient analysis of power system and micro-grid so chosen for this transient analysis study. A short circuit analysis is calculated based onIEC Std. 60909 using ETAP. This paper presents a simulated model of micro-grid with actual system oriented results and analyzes responses of system during fault conditions and various contingencies.

A rigid approach to short circuit analysis for large-scale distribution systems is introduced. The approach uses an individual (a-b-c) phase-based system representation, a nontrivial transformer model, and includes the contribution due to load. The method can, therefore, be applied to balanced or unbalanced, radial, network, or mixed-type distribution systems. This approach is oriented toward applications in distribution system operation analysis rather than the more typical planning-oriented analysis. The solution method is an iterative compensation method, which uses a single optimally ordered factorization of the bus admittance matrix (Y/sub Bus/), commonly used in power flow analysis, to simulate the fault condition. The use of this method in a short circuit analysis program enables a factorized Y/sub Bus/ solution, resulting in many advantages. Using a common factorization, both power flow and short circuit analyses are possible in a single execution. Since the factorization is unchanged, multiple faults of various types can be simulated in one run of the program. >

Short circuit calculations in distribution systems are performed using the traditional method of symmetrical components. However, this representation losses accuracy when the system is intrinsically unbalanced, as it is recognized for the case of distribution systems. This paper describes a methodology - implemented in MATLAB - that makes possible the analysis of short circuit for distribution networks without the use of symmetrical components. The elements in the distribution system are represented in the "phase domain" by their corresponding three phase impedance matrices. These element-matrices are used to construct two topologically based matrices that represent the entire network. General relationships between different types of fault and these network matrices are presented allowing the calculation of short circuit in the phase domain. The proposed method has shown to be very fast and robust. It has been tested using modified IEEE benchmark distribution systems and compared against commercial products using symmetrical components.

The use of distributed generation (DG) within distribution systems has increased for the last two decades due to institutional requirements and technical advances. This study presents the impact of DG in different types of distribution systems in terms of voltage profile and short circuit analysis. Test systems representing three types of distribution systems (radial, loop and network) are simulated using the simulation tool of Powerfactory-DigSilent while changing the location and penetration level of DG in the system. The results are useful in better understanding the system impact of DG.

The short-circuit current contribution of wind turbines has not received much attention so far. This paper establishes the doubly fed induction generator mathematical model and carried on corresponding short circuit analysis. Regarding the sudden short circuit process as a superimpose of steady state operation and transient state operation provoked by reverse voltage, stator three-phase short circuit current expression is obtained by carrying on the Laplace transformation and the inverse transformation to the state space equation. And the expression is confirmed by simulation. In addition, the character and attenuation rule of stator short circuit current component are analyzed, and maximum resistance of short circuit protective device is set.

In this paper, the characteristics analysis of a high-speed permanent magnet synchronous generator (PMSG) was performed considering saturation reactance. The equivalent circuit method (EMC) is a method for predicting performance in the design process of a generator. When using EMC, if the inductance of the equivalent circuit is not considering saturation, it is difficult to predict the performance of a generator accurately. Therefore, we applied a reactance that considered saturation to derive more accurate performance prediction through short-circuit analysis. The proposed method was verified using finite element method.

Development of electrical power system is linear with the increasing number of Distribution Generation (DG), which is change the pattern of power system protection due to the power flow and short circuit, especially in meshed distribution system. The analysis of short circuit is needed to obtain a reliable power system protection. This paper proposed Chaotic Firefly with tent map algorithm (CFA) method to get the minimum overcurrent relays time operation using the inverse time current characteristic. The proposed method had been compared with Firefly Algorithm (FA) in IEEE -9 bus with two DG. The result of total relay time operation using Chaotic Firefly with tent map algorithm is 3.557 seconds which is faster than another method.

Fault analysis of unbalanced radial and meshed distribution system with inverter based distributed generation (IBDG)

High penetration level of rooftop small-scale renewable energy generation (REG) such as solar and wind power into the existing low voltage (LV) network would cause the flow of power in reverse direction. This would also vary the level of short-circuit current required for relays to operate. Relay settings would be required to properly detect the unpredictable fault current and isolate the faulty section. This paper investigates the impact of residential distributed generation (DG) penetration level on the typical UK low voltage network protection system. Studies were commenced to properly charge and discharge the home connected energy storage battery (ESB). ESB is used as a remedial measure to confine the flow of reverse power due to rooftop DGs. Penetration level DGs are modeled based on proper ESB charging and discharging states in daily load cycle. Short circuit analysis is simulated on Matlab/Simulink. The power flow from the transformer secondary is managed to avoid malfunctioning of relays according to daily load cycle. Short circuit analysis results are compared with the UK passive network to investigate the impact of the DG on the short circuit currents at distribution transformer.

Ship DC power system, which is a kind of common DC bus system based on multiple VSCs, has been more and more popular because of its high efficiency. However, this common DC bus system can hardly balance the fast and selective protection requirements, especially in low-voltage high-capacity situations, which should be extensively protected by quick-fuses. In view of this kind of system, this paper analyses the short-circuit current calculation method of various faults and calculates a typical ship study example by transient simulations. On the basis of short-circuit calculation, the parameters of the fuses are designed based on fast and selective protection principles. At last, the real-ship multi-working condition short-circuit tests are carried out to verify the protection theory.

The high frequency of short circuit current fault in power grid PT. Badak NGL Bontang in 2017 becomes a serious problem. One of them is the Short Circuit at Distribution Transformer 48-PT-33-7 which resulted in a feeder 48-FDR-33 trip and cut off the power to all connected loads. This research is conducted to know the value of short circuit current fault by manual calculation and compared with the simulation software ETAP 12.6 which made system modeling refers to real network configuration in the field. After that, ETAP conducted simulation and short circuit analysis in transformer 48-PT-33-7. The calculation result is known that the short circuit current value between manual calculation and ETAP simulation is relatively same, ie 553,8 A / 555 A (one phase to ground), 891,47A / 885 A (two phase), 918,16 A / 950 A (two phase to ground), 1029.41 A / 1022 A (three phases). From the simulation also known the coordination sequence of the protection system works properly when the fault occurs. So from these two results indicate that the installed protection system is in accordance with the standard in securing the power grid from short-circuiting current fault.

Several large scale offshore wind farms are planned to be built far from the shores in the future. High Voltage Direct Current (HVDC) Light by ABB is an effective and reliable way to integrate this large scale wind power production to the grid. An expensive component of offshore wind park HVDC Light technology is offshore AC collector platform. The AC collector platform in the offshore wind farm HVDC link contributes significantly to the cost of the overall project. This paper investigates the comparison between two different AC topologies of an offshore wind farm connection to offshore HVDC converter platforms with and without offshore AC collector platforms. The technical feasibility of the omission of an AC collector platform from offshore wind farms connection to HVDC converter platform is investigated for the first time. In the first topology, the offshore wind farms are connected to an HVDC converter platform through offshore AC collector platforms. An offshore AC collector platform is used to collect energy from the wind farm and step up the voltages for transmission to offshore HVDC converter platform. The offshore AC collector platforms contribute significantly to the total cost and technical complexity of the HVDC connection. In the second topology, the offshore AC collector platform is removed from the circuit and the offshore wind farms are connected directly to offshore HVDC converter platform. The topological alteration of an offshore wind farm HVDC link gives rise to some technical challenges. The short circuit analysis and annual energy loss analysis is performed for these two topologies. The type of wind turbine generators, internal wind farm voltages and the distance between the wind farms and offshore HVDC converter platform are quite important factors that are investigated in this study. The short circuit analysis and loss analysis is performed for two types of wind turbine generators i.e. doubly fed induction generators (DFIG) and full conversion (FC) generators. Two internal wind farm voltage levels i.e. 33 kV and 66 kV, and three different distances i.e. 1 km, 5 km, and 10 km between the wind farms and offshore HVDC converter platform are investigated.

In this work, a method of optimal relay coordination for improving system reliability has been presented in association with the Wind Energy Conversion System (WECS). The graphical method as well as changes in Plug Setting Multiplier (PSM) and Time Dial Setting (TDS) have been used to test the system’s reliability with the help of ETAP. Load flow analysis, short circuit testing under different fault conditions, reliability assessment, and relay coordination have been performed on the proposed WECS. In this research work, a test system with relay coordination is proposed that is used for transformer protection using over-current relays (OCR) and ground-fault relays (GFR) devices with a wind energy induction generator. It is shown that coordination is off when WECS is added to the system. Therefore, maximum values of the circuit breaker’s trip device setting, the relay’s pickup, and the time dial settings are desirable to increase the coordination. Further, it has been revealed that the comprehensive analysis of load flow analysis, short circuit analysis, and reliability assessment play vital roles in achieving suitable relay coordination. Also, the use of ETAP software in this analysis improves the accuracy and speed of the circuit breaker operation at a reduced cost.

For short-circuit analysis in industrial and commercial power systems, a new approach of the ohmic method in such a form as to facilitate, as far as possible, its use and the realization of its evaluation is suggested. The 'characteristic' current method, by replacing the impedance of each equipment with the corresponding value of the 'characteristic' current, permits the application of the impedance properties to the inverse of the current values, either in meshed or nonmeshed networks. In order to achieve the correct design, rating and protection coordination of the whole power system, it is necessary to know and calculate step by step the values of short circuit current for each system component, from the utility or local generating connection point until the branch-circuits and the utilization equipments. The proposed approach assumes the above mentioned short-circuit current directly as calculation and comparison parameters. With the 'characteristic' currents as parameters the short-circuit analysis of substantial radial systems is made easier and a better matching of power system design requirements is permitted. >

Due to the fast growth of renewable energy technology, the electric power system is currently comprised of various renewable sources of energy. Renewable energy incorporation into the existing grid diminishes system strength at the point of common coupling, compromising grid reliability and security. The Short Circuit Ratio (SCR) is a commonly used metric for determining the strength of a system. To reduce voltage loss and to ensure effective operation of the protective devices during fault conditions, a minimum value of SCR is mandatory. In the case of high renewable penetration, this paper proposes short circuit ratio constrained economic dispatch to ensure power grid safety. Here, we formulate an optimization problem subject to various practical constraints, which is solved in GAMS using a quadratic programming model. GAMS provides us with the results of the power sharing of the generators. The obtained results are evaluated using a modified IEEE 39 bus test system in DIgSILENT PowerFactory. Load flow and short circuit analysis done in DIgSILENT PowerFactory proves the validity of the simulation results. The results satisfy the SCR constraint in addition to fulfilling other constraints.